Apparatus Having A Bioreactor And Membrane Filtration Module For Treatment Of An Incoming Fluid

ABSTRACT

An apparatus for treatment of an incoming fluid, comprising a bioreactor with a basin ( 2 ) with a fluid space and a membrane filtration module ( 12 ) comprising a housing ( 13 ) with one or more incorporated membranes ( 14 ), an inlet side, a permeate side and a retentate side, wherein the housing ( 13 ) delimits a connection chamber ( 18 ) on the inlet side of the membranes ( 14 ) into which a fluid inlet line ( 10 ) discharges which is connected to the fluid space of the basin ( 2 ). A closable flushing discharge line ( 20 ) is provided which is connected on one side to the connection chamber ( 18 ) and on the other side discharges outside the fluid space. A fluid mixture feed-through line from the basin to the connection chamber is closable, and a control unit ( 23 ) is provided for periodically closing the fluid mixture feed-through line and opening the flushing discharge line ( 20 ), and vice versa, for periodic flushing of at least the inlet side of the membranes ( 14 ) and the connection chamber ( 18 ) disposed underneath it.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage of International Application No.PCT/NL2007/000136, filed May 29, 2007, which claims the benefit ofNetherlands Application No. NL 1031926, filed May 31, 2006, the contentsof which is incorporated by reference herein.

FIELD OF THE INVENTION

The invention relates to an apparatus for treatment of an incomingfluid, comprising a bioreactor and a membrane filtration module, alsoreferred to as membrane bioreactor (MBR).

BACKGROUND OF THE INVENTION

A membrane bioreactor is known, for example, for purifying waste water,and comprises a basin which is partially filled with active sludge.During operation, the waste water is fed to the basin where it mixeswith the sludge. The active ingredients in the sludge take care ofpurifying the waste water. This process is accelerated even more bysupplying a gas, usually air, from below to (part of) the basin. Themixture of sludge and waste water is then fed to the membrane filtrationmodule where purified water is discharged as permeate, while theretained liquid, polluted particles and sludge particles as retentateare fed back to the basin. The membrane bioreactor is able to work witha high concentration of sludge particles, especially compared to aconventional system in which the bioreactor is combined with a settlingtank. As a result, the discharged purified water can be of high quality,and it is even readily possible to use the membrane bioreactor fortreating heavily polluted sewage water and/or streams of industrialwaste water.

The known membrane bioreactors can be divided into two groups, i.e.: adry-pit system or a submerged system. With the dry-pit system, amembrane filtration module is placed outside the basin of thebioreactor. With the submerged system, membranes are suspended insidethe basin of the bioreactor. In recent years, both systems havedeveloped in such a way that they show an increasing number ofsimilarities. Thus, for example, the membranes of the submerged systemare more and more often accommodated in a housing provided with inletand outlet apertures, which housing is then suspended in the basin likea box. In addition, there is a development taking place where more andmore facilities are being placed around these boxes which are intendedto supervise the flow past these membranes in order to optimize theperformance of these membranes. This has resulted in a membranefiltration module for the purpose of the submerged system which is orwill be increasingly similar to a membrane filtration module in thedry-pit system.

An example of a submerged system with flat membrane panels in atreatment tank is disclosed in EP 0 510 328. An example of a dry-pitsystem with tubular membranes which are accommodated in a membranefiltration module is disclosed in U.S. Pat. No. 5,494,577.

For both systems, it is disadvantageous that the membrane surfaces canbecome soiled quickly and that the flow passages inside the membranesand/or between and/or around the membranes often become blocked withforeign particles in the liquid stream during operation. This soilingand/or these blockages are caused by all kinds of particles which areentrained with the waste water, such as hairs, threads, etc. The soilingand/or the blockages may also be caused by biologically, physically orotherwise deformed particles which result from the reactions between thesludge and the waste water. Another possibility is that soiling mayprecipitate or blow or otherwise end up in the basins which are usuallyopen to the elements. The direct consequence of the soiling and/or theblockage of the flow passages is the loss of effective membrane surface.In addition, it results in the distribution of the liquid stream acrossthe flow passages no longer being homogeneous. This non-homogeneousdistribution leads to large variations in the liquid velocity and theturbulence thereof along the flow passages, as a result of which a crustof particles may form along the membrane surfaces. This in turn leads toa greater risk of blockage of (a part of) the flow passages, as a resultof which the liquid distribution may become disturbed even further. As aresult, an increasing amount of effective membrane surface is lost andan increasing amount of energy has to be supplied in order to maintainthe through-flow through the flow passages which are increasinglydifficult to flow through.

In order to prevent the flow passages from becoming soiled and/orblocked, it is known to use a filter upstream of the membrane filtrationmodule in order thereby to catch particles. However, it has been foundthat thread-like particles are still able to slip through the filter,and then still cause the abovementioned problems. Furthermore, it hasbeen found that the encrusted particles in the membrane filtrationmodule are very difficult to remove, and that they can damage themembrane material. If soiling is observed with the known systems, thenthe soiled membrane filtration module is disconnected, connected to acleaning unit and cleaned manually or semi-automatically. In this case,it is common practice for the blocked flow passages to be flushed backregularly with a cleaning liquid. This procedure usually takes up 10 to20% of the operating time of a membrane filtration module. Thepossibility and the frequency thereof is dependent on the type ofmembrane filtration module and is usually in the order of magnitude ofone to 60 minutes. In addition, the membrane filtration module can alsobe cleaned using a chemical cleaning liquid. This entire process takesas much as half an hour to a few hours per membrane filtration moduleand is again carried out at a frequency of once a day to once a week, oronce a month to once a year, depending on the membrane filtration moduleand operation. If desired, the membrane filtration module can be opened,the blocked membranes can be removed therefrom and the soiling can thenbe removed using brushes, jets of water or any other mechanicalancillary means. This cleaning method takes even more process time andis generally very labour-intensive and is only carried out in cases ofextreme soiling and/or blockage. If, in addition, a filter havingopenings smaller than 5 mm, or more commonly smaller than 3 mm andpreferably smaller than 1 mm is used upstream of the membrane filtrationmodule, then this filter has to be cleaned very regularly. An apparatusfor treatment of a fluid is known from DE 2196 20 246.

SUMMARY OF THE INVENTION

It is an object of the present invention to at least partially overcomethe abovementioned drawbacks and/or to provide a usable alternative. Inparticular, it is an object of the invention to provide an efficientmembrane bioreactor which is less affected by soiling and/or blockage.

This object is achieved by the apparatus according to the presentinvention. The apparatus in this case comprises a bioreactor having adry-pit or submerged membrane filtration module, which module isprovided on the inlet side, where a connection chamber is left clear,with a discharge line which discharges outside the fluid space. Thedischarge line is provided with a controllable closing element. A fluidmixture feed-through line from the fluid space of the basin to theconnection chamber is also provided with a controllable closing element.In addition, a control unit is provided for closing the fluid mixturefeed-through line and opening the discharge line at the desired moment,and vice versa. As a result thereof, it is advantageously possible toautomatically flush at least the inlet side of the membrane and theconnection chamber beneath it. During flushing, soiled and encrustedparticles are released from the inlet side and/or from the surfaces ofthe membranes and are discharged outside the fluid space via the opendischarge line. When flushing has finished, for example after a presetperiod of time has lapsed, the treatment process can be resumedimmediately, by again closing the discharge line and opening the fluidmixture feed-through line.

It has been found in practice that the flushing step advantageously, ifrepeated regularly, after a certain period of normal operation of theapparatus, ensures that the pressure on the inlet side of the membranefiltration module can remain stable for a long period of time. This isconnected with the fact that the flushing step ensures that the soilingand/or blockages of the flow passages of the membranes is/are cleanedaway in an efficient manner. Furthermore, it has been found that theflushing step leaves the membrane surface, the flow passages, as well asthe inlet side of the flow passages intact.

The succession of a period of fluid treatment and a period of flushingis referred to in this case as a filtration cycle. After a number ofsuch filtration cycles, it is possible to use other cleaning methods inorder to further improve the membrane performance. Consideration may begiven to flushing the module with supplied pressurized air, the use ofchemical cleaning agents, and/or disassembling the membrane filtrationmodule in order to be able to clean the parts separately.

In accordance with a particular embodiment, the control unit is equippedwith a counter for periodically initiating the flushing step. Thecounter may in this case be set to a value of between 0.1-1000 hours, inparticular between 0.2-1000 hours, or more in particular between 1-24hours. When the counter reaches the preset value, the control unitensures that the fluid mixture feed-through line is closed and thedischarge line opened.

In another embodiment, the control unit is designed in order to startthe flushing process in dependence on measurement values relating to theperformance of the membrane filtration module. This may, for example, bemeasuring pressure at certain positions within the membrane filtrationmodule or recording the amount of energy which is required in order topass the fluid through the flow passages of the membranes. A combinationof initiating mechanisms is likewise possible.

The time which is required for the flushing step can be made dependenton the observed soiling and/or blockages in the flow passages, but mayalso be set to a fixed value.

In one particular embodiment, the closable fluid mixture feed-throughline is formed by the fluid inlet line which discharges into theconnection chamber of the membrane filtration module. To this end, thefluid inlet line is provided with a controllable closing element. Thisembodiment is in particular advantageous in combination with a dry-pitmembrane filtration module. In a variant thereof, the membranefiltration module is submerged in the fluid space of a sub-basin. Inthis case, the connection chamber of the membrane filtration module isthen provided with one or more inflow openings. The closable fluidmixture feed-through line can in this case be formed by a flowconnection between the fluid space of the basin and the fluid space ofthe sub-basin. This flow connection may then be provided with acontrollable closing element.

In a preferred embodiment, it is possible to provide a controllableflushing liquid feed line on the permeate side and/or retentate sideand/or on the connection chamber of the membrane filtration module. Thisflushing liquid can then ensure that a more thorough flushing anddischarging of the soiling and/or blockages to beyond the fluid spacetakes place during the flushing step. Depending on the observed soilingor blockage, the flushing liquid can be supplied at a significantlyhigher pressure than the fluid pressure in the module during treatment.In particular, the flushing liquid pressure may be more than 1-20 timeshigher than the fluid pressure during operation, more particularly morethan 3-10 times higher.

In a variant or in addition to supplying flushing liquid, the fluidwhich is already present within the membrane filtration module canadvantageously also be used. For example, if the flow passages of themembranes have a length of 1-6 metres and these flow passages arearranged in the vertical direction above the connection chamber, thereis more than sufficient fluid pressure in these flow passages as aresult of the force of gravity. This fluid pressure ensures that theflow passages and the connection chamber are automatically flushed withthe fluid which is inside the flow passages as soon as the fluid mixturefeed-through line is closed and the discharge line is opened.

The slurry which has been discharged via the discharge line to beyondthe fluid space can be collected in an external settling tank andsubsequently be fed back to the basin of the bioreactor, optionallyafter further purification by means of a filter. Thus, it isadvantageously possible to maintain the concentration of treatment fluidin the bioreactor at the desired level. This may in practice alsoadvantageously ensure a periodical cleaning of the treatment fluid insuch a manner that periodical cleaning or changing of the entire amountof treatment fluid in the basin is no longer required. Thissignificantly reduces the down time of the apparatus. It is alsopossible to discharge (part of) the slurry to the outside. However, inthat case treatment fluid will have to be supplied to the basinregularly as a compensating measure.

In a preferred embodiment, gas distribution means are provided whichdischarge into the connection chamber of the membrane filtration module.During the fluid treatment, these gas distribution means supply gasbubbles which also ensure that the fluid is conveyed through the flowpassages of the module. Advantageously, it is also possible to clean thegas distribution means during the flushing step, for example bytemporarily increasing the gas supply pressure. Thus, it is preventedthat the gas distribution means require an increasingly high pressure inorder to be able to supply gas during the fluid treatment. Otherpossibilities of cleaning these gas distribution means are flushing witha fluid, for example permeate or a liquid to which cleaning chemicalshave been added.

Further preferred embodiments of the invention are describedhereinafter.

The invention also relates to a method for cleaning the membranes andthe inlet side of a membrane filtration module of an apparatus accordingto the invention, as well as to the use of such an apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail with reference to theattached drawings, in which:

FIG. 1 shows a diagrammatic view of an embodiment of the apparatusaccording to the invention with a dry-pit membrane filtration module;

FIG. 2 shows a view corresponding to that of FIG. 1 with submergedmembrane filtration modules;

FIG. 3 shows a part view of FIG. 1 of a first variant embodiment of themembrane filtration module;

FIG. 4 shows a view corresponding to that of FIG. 3 of a second variantembodiment;

FIG. 5 shows a view corresponding to that of FIG. 3 of a third variantembodiment;

FIG. 6 shows a diagrammatic view in more detail of a variant embodimentof FIG. 1;

FIG. 7 shows a diagrammatic view of a membrane filtration module withplate-shaped membranes;

FIG. 8 shows a view corresponding to that of FIG. 7 with tubularmembranes placed in a row;

FIG. 9 shows a view corresponding to that of FIG. 7 with bundled tubularmembranes; and

FIG. 10 shows a greatly magnified bottom view of an exploded membranefiltration module with several bundled tubular membranes.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In FIG. 1, the apparatus for treatment of a fluid is denoted overall byreference numeral 1. The apparatus 1 comprises a bioreactor with a basin2 with a fluid space which contains a biomass, in particular activesludge. A fluid feed line 3 opens into the basin 2 via which fluid feedline 3 raw waste water is passed to the basin 2. In the fluid feed line3, there is a filter 4 by means of which a first purification of thewaste water is carried out. This may be a filter with one specific meshwidth or a range of different mesh widths. In the basin 2, the wastewater mixes with the active sludge, as a result of which a fluid mixture5 is formed. First gas distribution means 7 discharge into the bottom ofthe basin 2 via which gas distribution means 7 gas is added to (part of)the fluid mixture 5. In the fluid mixture 5, the waste water is cleanedfurther by means of, inter alia, aerobic reactions with the activesludge particles. Depending on the geometry of basin 2, the location ofthe gas distribution means 7, and the flow patterns in basin 2,different reaction zones may result. The fluid mixture 5 is supplied toa membrane filtration module 12 via a fluid inlet line 10. It ispossible to incorporate another filter in this feed line as well inorder to recover soiling components which have not been recovered beforeand/or which were formed during the reactions. The membrane filtrationmodule 12 comprises a housing 13 in which there is a membrane surface14. On the permeate side of the membrane 14, a permeate discharge line15 is provided. On the retentate side of the membrane 14, a retentatedischarge line 16 is provided. The retentate discharge line 16 opensinto the basin 2. On the inlet side of the module 12, that is to saywhere the fluid inlet line 10 joins the housing 13, there is aconnection chamber 18. Second gas distribution means 19 discharge intothe bottom of the connection chamber 18. These ensure that the membranesurface 14 is kept clean by means of treatment with gas during fluidtreatment, and ensure that the fluid mixture is conveyed along andthrough the membrane surface 14.

According to the invention, the connection chamber 18 is provided with adischarge line 20. The discharge line 20 is provided with a controllableshut-off valve 21. The fluid inlet line 10 is likewise provided with acontrollable shut-off valve 22. A control unit 23 is provided forcontrolling the shut-off valves 21 and 22. Following a period of fluidtreatment in which clean water is discharged via the permeate dischargeline 15, and in which retained fluid is fed back to the basin 2 via theretentate discharge line 16, according to the invention a flushing steptakes place in each case by means of a suitable actuation of theshut-off valves 21 and 22 via the control unit 23. In this case, theshut-off valve 22 of the fluid inlet line 10 is closed and the shut-offvalve 21 of the discharge line 20 is opened. The fluid which is insidethe membrane filtration module 12 (on the retentate side) is then freeto flow away in a downwards direction in one go via the connectionchamber 18 towards the open discharge line 20. This sudden downwardsflow ensures in a very efficient way that the soiling components insidethe membrane filtration module 12, both along the membrane surface andin the connection chamber 18, are discharged outside the module 12. Assoon as this flushing process has finished, the control unit 23 makessure that the shut-off valve 21 of the discharge line 20 is closedagain, and the shut-off valve 22 of the fluid inlet line 10 is reopened.Then, another fluid treatment can be carried out, following whichanother flushing step can be carried out, etc.

The discharge line 20 ends above a settling container 25. The contentsof this settling container 25 can be discharged to an externalreceptacle at set times. It is also possible to feed the contents of thesettling container 25, or part thereof, back to the basin 2 via asediment discharge line 26. The sediment discharge line 26 mayoptionally be provided with a filter 27.

The basin 2 is also provided with a drain discharge line 29 via which,usually in a discontinuous manner, sludge can be drained.

FIG. 2 shows a variant with two submerged membrane filtration modules.Identical components are in this case denoted by the same referencenumerals as in FIG. 1. The apparatus comprises a separate sub-basin 34with a fluid space which is in flow connection with the fluid space inthe basin 2 via supply and discharge lines 35, 36. Two membranefiltration modules 38 are submerged in the fluid space of the sub-basin34. Each membrane filtration module 38 comprises a surrounding housing40 containing the membrane surface 14. At the bottom side, the housing40 delimits a connection chamber 42 which is in turn provided with aclosable discharge line 20 which discharges outside the fluid space ofthe sub-basin 34. The location of the fluid inlet line cannot bespecified as clearly as is the case with a dry-pit embodiment, and formspart of one or more inflow openings in the connection chamber 42 inwhich the fluid mixture from the sub-basin 34 mixes with gas which hasbeen introduced by the gas distribution means 19, which mixture thenpasses along and through the membrane surface 14. The exact design ofthe fluid inlet line depends on the embodiment of the submerged membranefiltration module 38.

The feed line 35 is provided with a controllable shut-off valve 43.Following a period of fluid treatment, a flushing step can then becarried out by means of a suitable actuation of the shut-off valves 21and 43 via the control unit 23. In this case, the shut-off valve 43 ofthe feed line 35 is closed and the shut-off valves 21 of the dischargelines 20 are opened. The fluid which is in the sub-basin 34 and insidethe membrane filtration modules 38 is then free to flow away in adownwards direction in one go to the open discharge lines 20 via theconnection chambers 42. The fluid mixture level in the sub-basin 34 willin this case fall to the level of the connection chambers 42, as thedischarge lines 20 start at the connection chambers 42. If desired, thedischarge lines may also start at a lower level and/or be provided withinflow openings at a lower level, so that the sub-basin 34 can emptyfurther or even completely. As soon as the flushing process hasfinished, the control unit 23 again ensures that the shut-off valves 21are closed, and the shut-off valve 43 is opened.

FIG. 2 furthermore shows that an additional prefilter 45 is provided atthe top of the connection chamber 42, in order to protect the inflowside of the membranes which are inside the membrane filtration moduleagainst blockage. This additional prefilter 45 will also be flushedclean in an efficient manner during each flushing step, after which theresulting slurry is discharged via the discharge line 20. The prefilter45 can supplement or even take over the function of any filter in thefeed line 35.

For the flushing step, the embodiments of FIGS. 1 and 2 use the fluidwhich is in the membrane filtration modules. With the variant shown inFIG. 3, a controllable flushing liquid feed line 50 is provided inaddition thereto and is connected to the permeate side of the module 12.During the flushing step, the shut-off valve 51 of the flushing liquidfeed line 50 is temporarily opened by the control unit. As a resultthereof, the space inside the module 12, including the membrane surfaces14 and the connection chamber 18 are cleaned further by flushing. FIG. 4shows a variant in which the closable flushing liquid feed line 50 isconnected to the retentate side of the module 12. FIG. 5 shows a variantin which the closable flushing liquid feed line 50 is connected to theconnection chamber 18 of the module 12. With these variants as well, afurther improvement of the flushing step can be achieved. It is alsopossible to provide a combination of the flushing liquid feed linesshown in FIGS. 3-5, so that, depending on the soiling and/or blockageobserved, one or more of these flushing liquid feed lines can be opened.

FIG. 6 shows a variant of FIG. 1 in which identical components aredenoted by the same reference numerals. Only the differences will bebriefly discussed below. The first gas distribution means are in thiscase formed by a distribution panel provided with a plurality of outflowopenings which extends over the bottom of the basin 2 and is connectedto a ventilator 60. In order to be able to pass the fluid mixturethrough the membrane filtration module 12 with greater force, a pump 62is provided in the closable fluid inlet line 10. The second gasdistribution means 19 in the connection chamber 18 are supplied with agas via a ventilator 64. A controllable shut-off valve 65 is providedbetween the ventilator 64 and the second gas distribution means 19. Themodule 12 is provided with two membrane panels 14 between which a flowpassage 68 is left clear which forms the retentate side. At its top,this flow passage 68 opens out into a chamber 69 which is connected tothe fluid space in the basin 2 via the retentate discharge line 16. Theretentate discharge line 16 is furthermore provided with a branch 70 fordischarging retentate to another location, if desired.

On the outside of the membrane panels 14 is the permeate side 72 towhich the permeate discharge line 15 is connected. The permeatedischarge line 15 is provided with a controllable shut-off valve 74, viawhich the permeate discharge line 15 can be closed during the flushingstep, if desired. Furthermore, the permeate discharge line 15 comprisesa pump 75 for pressurized discharge of the cleaned fluid. The cleanedfluid can then be discharged to a receptacle 76 and/or to an externallocation (not shown in any more detail). From the receptacle 76, thetreated fluid can be supplied as flushing liquid to the module 12 viathe flushing liquid feed line 50 during the flushing step. In order tobe able to supply the flushing liquid at sufficient pressure, a pump 78is provided.

The settling container 25 is provided with a closable sediment dischargeline 80. Furthermore, the sediment discharge line 26 leading back to thebasin is provided with a pump 81, and the sediment discharge line 26 nowdischarges into the filter 4 provided in the fluid feed line 3. Thus, ahighly multifunctional treatment apparatus is achieved, in which use ismade of treated fluid and discharged retentate or slurry, respectively,in an efficient way.

FIG. 7 shows a variant of a membrane filtration module, in whichidentical components are again denoted by the same reference numerals asin the preceding figures. It can clearly be seen that the membranes 14in this case are of the flat plate-shaped type. The prefilter 45 whichis provided at the top of the connection chamber 18 can also clearly beseen.

FIG. 8 shows a variant of FIG. 7 in which the membranes 14 comprise aplurality of hollow fibres or capillaries placed in rows next to oneanother.

FIG. 9 shows a variant of FIG. 7 in which the membranes 14 comprise aplurality of hollow fibres or capillaries arranged in bundled form.

If several hollow fibres or capillaries or tubelets placed next to oneanother are used as membranes, in particular in a bundled form, thenthese can together advantageously form a prefilter. This can render thefunction of the prefilter 45 provided in FIG. 9 and/or the possiblefilter in the fluid inlet line mentioned before obsolete orsignificantly facilitate the task thereof. Thus, for example, a largermesh width may then be selected for the prefilter 45. FIG. 10 shows theway the plurality of hollow fibres or capillaries or tubelets work as aprefilter.

Many variants are possible in addition to the embodiments illustrated.Thus, the membranes and/or the membrane filtration modules can bearranged both horizontally and vertically or in other positions. Withthe submerged variant, it is also possible to place the membranefiltration modules directly in the basin. If desired, a dividing wallcan be placed in the basin between the section where the membranefiltration module is disposed and the section where the incoming fluidflows in.

Furthermore, the invention can be used with all types of membranes,independent of their shape (for example, but not exclusively, flat or ofany possible diameter), filtration side (inner side or outer side) ormaterial (for example polymer or ceramic).

In addition, the invention can be used with any membrane process ofwhich a membrane bioreactor forms part. Currently, the most commonprocesses are those which are referred to as microfiltration orultrafiltration, but other membrane processes, such as nanofiltrationand reverse osmosis/hyperfiltration, are also possible.

Thus, according to the invention, a membrane bioreactor with asignificantly improved action has been provided due to the feature ofperiodically flushing the membrane filtration modules and, if desired incombination with the former, the gas distribution means with dischargeline to outside the fluid space. The flushing step is advantageouslycombined with the integrated cleaning of the treatment fluid and theperiodic draining thereof, respectively.

1-36. (canceled)
 37. An apparatus for treatment of an incoming fluid,comprising: a bioreactor with a basin with a fluid space that is meantto be at least partially filled with a treatment fluid; a fluid feedline discharging into the basin for feeding, during operation, theincoming fluid to the treatment fluid and mixing and treating it withthe latter so as to obtain a fluid mixture; and a membrane filtrationmodule comprising a housing with one or more incorporated membranes, aninlet side, a permeate side and a retentate side, wherein the housingdelimits a connection chamber on the inlet side of the membranes intowhich housing a fluid inlet line discharges which is connected to thefluid space of the basin, the housing further comprises a permeatedischarge line connected to the permeate side and a retentate dischargeline connected to the retentate side, a closable flushing discharge lineis provided which is connected on one side to the connection chamber andon the other side discharges outside the fluid space, and a fluidmixture feed-through line from the basin to the housing is closable, thefluid inlet line discharges into the connection chamber to which theclosable flushing discharge line is also connected, and a control unitis provided for periodically closing the fluid mixture feed-through lineand opening the flushing discharge line, and vice versa, for periodicflushing of at least the inlet side of the membranes and the connectionchamber disposed underneath it.
 38. The apparatus according to claim 37,wherein the closable fluid mixture feed-through line is formed by thefluid inlet line which is provided with a closing element and whichdischarges into the connection chamber.
 39. The apparatus according toclaim 37, wherein a flushing liquid feed line controllable by thecontrol unit is connected to the permeate side of the membranefiltration module.
 40. The apparatus according to claim 37, wherein aflushing liquid feed line controllable by the control unit is connectedto the retentate side of the membrane filtration module.
 41. Theapparatus according to claim 37, wherein an external flushing liquidfeed line controllable by the control unit is connected to the closablefluid mixture feed-through line.
 42. The apparatus according to claim37, wherein the flushing discharge line discharges into a settlingcontainer.
 43. The apparatus according to claim 42, wherein the settlingcontainer is provided with a sediment discharge line leading back to thebasin.
 44. The apparatus according to claim 43, wherein the sedimentdischarge line from the settling container to the basin passes through afilter.
 45. The apparatus according to claim 42, wherein the settlingcontainer is provided with a sediment discharge line to an externalsystem other than the basin.
 46. The apparatus according to claim 37,wherein the retentate discharge line leads back to the basin.
 47. Theapparatus according to claim 37, wherein first gas distribution meansare provided which discharge at the bottom of the fluid space of thebasin.
 48. The apparatus according to claim 37, wherein second gasdistribution means are provided which discharge into the connectionchamber of the membrane filtration module.
 49. The apparatus accordingto claim 48, wherein a flushing liquid feed line controllable by thecontrol unit is connected to the gas distribution means.
 50. Theapparatus according to claim 49, wherein a compressed air line isconnected to the flushing liquid feed line.
 51. The apparatus accordingto claim 50, wherein a line carrying an external flushing liquid isconnected to the flushing liquid feed line.
 52. The apparatus accordingto claim 37, wherein the treatment fluid is biomass, in particularactive sludge.
 53. The apparatus according to claim 37, wherein themembranes have the form of plates.
 54. The apparatus according to claim37, wherein the membranes have the form of tubes.
 55. The apparatusaccording to claim 54, wherein the membranes comprise tubelets.
 56. Theapparatus according to claim 54, the membranes comprise capillaries. 57.The apparatus according to claim 54, wherein the membranes comprisehollow fibres.
 58. The apparatus according to claim 37, wherein themembrane filtration module is submerged in the fluid mixture duringoperation.
 58. The apparatus according to claim 37, wherein the fluidspace of the basin comprises a section separated off by a partition wallin which the membrane filtration module is provided.
 60. The apparatusaccording to claim 37, wherein a separate sub-basin is provided with afluid space which, via a feed line, is in flow connection with the fluidspace of the said basin, the membrane filtration module being providedin the fluid space of the sub-basin.
 61. The apparatus according toclaim 60, wherein the closable fluid mixture feed-through line is formedby the feed line between the basin and the sub-basin which is providedwith a closing device.
 62. The apparatus according to claim 37, whereinthe membrane filtration module is disposed outside the fluid space ofthe basin.
 63. The apparatus according to claim 37, wherein a pluralityof tubular membranes is bundled together, and wherein the inlet side ofthe bundle of tubular membranes forms a cleaning/filtering additionalfacility for the fluid mixture, in particular with filter operation. 64.The apparatus according to claim 37, wherein a cleaning/filteringadditional facility for the fluid mixture, in particular a filter, isprovided in the connection chamber on the inlet side of the membranes ofthe membrane filtration module.
 65. A method for cleaning the membranesand the inlet side of a membrane filtration module of an apparatusaccording to any of the preceding claims, which comprises the followingsteps: filling the basin with a treatment fluid; feeding an incomingfluid to the treatment fluid present in the basin and mixing andtreating it with the latter fluid so as to obtain a fluid mixture;feeding the fluid mixture to the membrane filtration module; dischargingpermeate filtered by and retentate retained by the membranes; andperiodically closing the fluid mixture feed-through line and opening theflushing discharge line, so that at least the inlet side of themembranes and the connection chamber of the membrane filtration moduledisposed underneath it are flushed.
 66. The method according to claim65, wherein the periodic closing of the fluid mixture feed-through lineand opening of the flushing discharge line is initiated by a counter, atime period, the local pressure and/or a calculated transmembranepressure differential.
 67. The method according to claim 65, whereinduring the periodic closing of the fluid mixture feed-through line andopening of the flushing discharge line a flushing liquid is delivered tothe permeate side of the membrane filtration module.
 68. The methodaccording to claim 65, wherein during the periodic closing of the fluidmixture feed-through line and opening of the flushing discharge line aflushing liquid is delivered to gas distribution means which dischargeinto the connection chamber of the membrane filtration module.
 69. Themethod according to claim 65, wherein during the periodic closing of thefluid mixture feed-through line and opening of the flushing dischargeline a flushing liquid is delivered to the retentate side of themembrane filtration module.
 70. The method according to claim 65,wherein during the periodic closing of the fluid mixture feed-throughline and opening of the flushing discharge line a flushing liquid isdelivered to the inlet side of the membrane filtration module.
 71. Themethod according to claim 65, wherein the step of feeding an incomingfluid to the treatment fluid present in the basin and mixing andtreating it with the latter fluid to obtain a fluid mixture takes placein a continuous process.
 72. Use of an apparatus according to claim 1for the purification of waste water.